CVE-2024-1813: Simple Job Board WordPress Plugin RCE Flaw

CVE-2024-1813 Overview

CVE-2024-1813 is a critical PHP Object Injection vulnerability affecting the Simple Job Board plugin for WordPress. The vulnerability exists in all versions up to and including 2.11.0 and stems from unsafe deserialization of untrusted input in the job_board_applicant_list_columns_value function. This vulnerability allows unauthenticated attackers to inject malicious PHP objects, potentially leading to severe consequences including arbitrary file deletion, sensitive data retrieval, or remote code execution when combined with an existing POP (Property Oriented Programming) chain from another installed plugin or theme.

Critical Impact

Unauthenticated attackers can exploit this PHP Object Injection vulnerability to potentially achieve remote code execution, delete arbitrary files, or exfiltrate sensitive data when a POP chain is present via additional installed components on the target WordPress system.

Affected Products

• Simple Job Board plugin for WordPress versions ≤ 2.11.0
• presstigers simple_job_board (all versions through 2.11.0)
• WordPress installations with Simple Job Board plugin installed

Discovery Timeline

• 2024-04-09 - CVE-2024-1813 published to NVD
• 2025-01-31 - Last updated in NVD database

Technical Details for CVE-2024-1813

Vulnerability Analysis

This vulnerability falls under CWE-502 (Deserialization of Untrusted Data), a well-known class of vulnerabilities that can have devastating consequences in PHP applications. The Simple Job Board plugin processes serialized data without adequate validation when handling job application submissions. When an administrator views a submitted job application, the plugin deserializes user-controlled input through the job_board_applicant_list_columns_value function without proper sanitization.

PHP Object Injection vulnerabilities are particularly dangerous because they can be chained with existing "magic methods" in other installed code to form a POP chain. If a suitable gadget chain exists within the WordPress installation—whether from the core, another plugin, or an active theme—attackers can leverage this deserialization point to execute arbitrary operations with the privileges of the web server.

The attack requires no authentication, making it accessible to any remote attacker who can submit job applications through the plugin's public-facing interface. The exploitation is triggered when an administrator views the malicious application in the WordPress dashboard.

Root Cause

The root cause of CVE-2024-1813 is the use of PHP's unserialize() function on untrusted user input within the job_board_applicant_list_columns_value function. The plugin fails to implement proper input validation or use safer alternatives like json_decode() for handling structured data. When serialized PHP objects are passed through this function, the deserialization process instantiates those objects and may trigger magic methods such as __wakeup(), __destruct(), or __toString(), which can be exploited if a suitable POP chain exists.

Attack Vector

The attack is network-based and can be executed by unauthenticated remote attackers. The exploitation flow involves:

1. An attacker crafts a malicious serialized PHP object containing a payload designed to exploit an existing POP chain
2. The attacker submits a job application through the plugin's public interface, embedding the serialized payload in application data fields
3. When a WordPress administrator views the submitted job application in the admin dashboard, the vulnerable job_board_applicant_list_columns_value function processes and deserializes the malicious input
4. If a compatible POP chain exists on the target system, the deserialization triggers the chain, allowing the attacker to execute arbitrary code, delete files, or access sensitive data

The vulnerability mechanism relies on unsafe deserialization practices in the plugin's job application handling functionality. When serialized data from job applications is processed without validation, malicious PHP objects can be instantiated. Technical details about the specific code changes can be found in the WordPress Changeset Update and the Wordfence Vulnerability Report.

Detection Methods for CVE-2024-1813

Indicators of Compromise

• Unusual serialized PHP object strings in job application database entries containing unexpected class names
• Web server logs showing POST requests to job application endpoints with serialized object patterns (e.g., O:, a:, s: sequences)
• Unexpected file modifications or deletions on the WordPress server
• Database entries containing base64-encoded or serialized payloads in job application meta fields
• Evidence of unauthorized code execution or new backdoor files in the WordPress installation

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block serialized PHP object patterns in HTTP requests targeting WordPress
• Monitor job application submissions for anomalous serialized data structures using regex patterns for PHP serialization
• Review WordPress access logs for suspicious activity patterns around job application submission and viewing endpoints
• Deploy file integrity monitoring to detect unauthorized changes to WordPress core, plugin, and theme files

Monitoring Recommendations

• Enable detailed logging for the Simple Job Board plugin and monitor for deserialization-related errors
• Set up alerts for unusual database queries or modifications to the wp_postmeta table related to job applications
• Implement real-time monitoring of PHP error logs for object instantiation warnings or fatal errors
• Monitor network traffic for data exfiltration attempts following job application viewing events

How to Mitigate CVE-2024-1813

Immediate Actions Required

• Update the Simple Job Board plugin to version 2.12.0 or later immediately
• Review existing job applications in the database for signs of malicious serialized payloads
• Audit installed plugins and themes to identify potential POP chains that could be exploited
• Implement a Web Application Firewall with rules to block serialized PHP object injection attempts
• Consider temporarily disabling the Simple Job Board plugin if immediate patching is not possible

Patch Information

The vulnerability has been addressed by the plugin developers. The security fix can be reviewed in the WordPress Changeset Update. WordPress administrators should update to the latest version of Simple Job Board through the WordPress plugin dashboard. The patch implements proper input validation and avoids unsafe deserialization of user-controlled data.

Workarounds

• If immediate patching is not possible, disable the Simple Job Board plugin until the update can be applied
• Implement server-level input filtering to block requests containing serialized PHP object patterns
• Restrict access to the WordPress admin dashboard using IP allowlisting to limit exposure
• Remove unnecessary plugins and themes that could provide POP chain gadgets for exploitation

# Configuration example - Block serialized PHP objects in Apache
# Add to .htaccess or Apache configuration
<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteCond %{QUERY_STRING} (O:|a:|s:)[0-9]+: [NC,OR]
    RewriteCond %{REQUEST_BODY} (O:|a:|s:)[0-9]+: [NC]
    RewriteRule .* - [F,L]
</IfModule>